High impact polystryene having high modulus and resistance to environmental stress cracking

ABSTRACT

High impact polystyrenes and related monovinyl aromatic polymers generally have either a high modulus or good resistance to environmental stress cracking. The present invention is directed at polymeric materials having both a high modulus and good resistance to environmental stress cracking thus enabling the down gauging of parts, and or the use of the materials in new applications. The invention is predicated on the use of one or more, or even all of the following features: a high molecular weight matrix polymer, reduced concentration of elastomeric polymer, or methods that result in large rubber particle size.

FIELD OF THE INVENTION

The invention is related to polymeric materials having good resistanceto environmental stress cracking. In particular, the invention isrelated to polymeric materials having improved balance of tensileproperties and resistance to environmental stress cracking so that costbenefits associated with down gauging can be achieved.

BACKGROUND OF THE INVENTION

Various approaches have been made to provide rubber reinforced monovinylaromatic polymers having good resistance to environmental stresscracking (i.e., good ESCR). These include the use of multi-layer sheettechnology, increasing the amount of rubber, increase gel phase volume,optimizing the rubber particle size, controlling the amount of crosslinking of the rubber, optimizing the process, the use of additives suchas polypropylene, polybutylene, and ethylene/α-olefin copolymers, andthe use of high molecular weight rubber. Some of these approaches andrelated technologies are described for example in US Patent ApplicationPublication Nos. US2011/0166295 A1 (published on Jul. 7, 2011),US2010/0197863 A1 (published on Aug. 5, 2010), and US2011/0218292 A1(published on Sep. 8, 2011); and U.S. Pat. No. 6,350,813 B1 (issued onFeb. 26, 2002), U.S. Pat. No. 4,144,204 (issued on Mar. 13, 1979), andU.S. Pat. No. 6,353,066 B1 (issued on Mar. 5, 2002), all incorporatedherein by reference in their entireties. However, these approaches havehad varying effects on other performance properties. For example, manyof these approaches require generally a high concentration of impactmodifier (rubber). In particular, when using low concentrations ofrubber and high concentration of monovinyl aromatic polymer matrix(e.g., in a reactor blend where one or more monovinyl aromatic monomersare polymerized in the presence of rubber), there is generally a need tomake low molecular weight monovinyl aromatic polymer matrix in order toobtain sufficiently large rubber particles for providing good ESCR.

Because of the low modulus of many compositions having good resistanceto environmental stress cracking, rigid parts made of these materialsare required to have generally thick walls. Thus, there continues to bea need for polymeric composition having a combination of good ESCR andhigh modulus, so that parts in existing applications can be down gaugedand/or so that the material can be used in new applications for rubberreinforced monovinyl aromatic polymer compositions. For example, suchimproved balance of ESCR and modulus may allow for down gauging ofliners used in refrigerators and freezers. There is also a need for suchimproved materials having one or more of (e.g., all of) the followingcharacteristics: high heat distortion temperature, good impact strength,good processability, low cost, high Vicat softening point, good tensileproperties, good tensile modulus, good flexural modulus, and the like.

SUMMARY OF THE INVENTION

One or more of the aforementioned needs are met using the compositionsaccording to the teachings herein. Preferred compositions have acombination of good resistance to environmental stress cracking and highmodulus.

One aspect of the invention is directed at a composition comprising: arubber-modified monovinyl aromatic polymer including about 90 weightpercent or more of a rigid monovinyl aromatic polymer matrix, based onthe total weight of the composition; and from about 2 to about 7.5weight percent of one or more elastomeric polymers, based on the totalweight of the composition. Preferably, the elastomeric polymer ispresent as grafted and occluded rubber particles dispersed within themonovinyl aromatic polymer matrix. The monovinyl aromatic polymer mayinclude one or more monovinyl aromatic monomers. The monovinyl aromaticpolymer preferably includes about 60 weight percent or more styrenemonomer, based on the total weight of the monovinyl aromatic polymer.The monovinyl aromatic polymer may have a sufficiently high molecularweight so that the ESCR elongation at break after 10 days in corn oil at1% strain is about 15% or more. Preferably, the molecular weight of themonovinyl aromatic polymer is characterized by a weight averagemolecular weight of 200,000 g/mol or more (more preferably 205,000 g/molor more), and a polydispersity index of about 2 or more.

Another aspect of the invention is directed at an article including acomposition according to the teachings herein. Preferred articlesinclude liners, such as liners for appliance.

Another aspect of the invention is directed at a process for preparing acomposition according to the teachings herein.

Another process related aspect of the invention is directed at a methodof forming an article using a composition according to the teachingsherein.

DETAILED DESCRIPTION

The explanations and illustrations presented herein are intended toacquaint others skilled in the art with the invention, its principles,and its practical application. Those skilled in the art may adapt andapply the invention in its numerous forms, as may be best suited to therequirements of a particular use. Accordingly, the specific embodimentsof the present invention as set forth are not intended as beingexhaustive or limiting of the teachings. The scope of the teachingsshould, therefore, be determined not with reference to the abovedescription, but should instead be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. The disclosures of all articles and references,including patent applications and publications, are incorporated byreference for all purposes. Other combinations are also possible as willbe gleaned from the following claims, which are also hereby incorporatedby reference into this written description.

As used herein, a “polymer” is a polymeric compound prepared bypolymerizing monomers, whether of the same or a different type. Thegeneric term polymer thus embraces the term homopolymer, usuallyemployed to refer to polymers prepared from only one type of monomer,and the terms copolymer and interpolymer as defined below.

As used herein, a “copolymer”, “interpolymer” and like terms means apolymer prepared by the polymerization of at least two different typesof monomers. These generic terms include the traditional definition ofcopolymers, i.e., polymers prepared from two different types ofmonomers, and the more expansive definition of copolymers, i.e.,polymers prepared from more than two different types of monomers, e.g.,terpolymers, tetrapolymers, etc.

As used herein, “blend”, “polymer blend” and like terms refer to acomposition of two or more compounds, typically two or more polymers. Asused herein, “blend” and “polymer blend” also includes “reactor blends,”such as where a monomer is polymerized in the presence of a polymer. Forexample, the blend may initially be a blend of a first polymer and oneor more monomers which are then polymerized to form a second polymer. Ablend may or may not be miscible. A blend may or may not be phaseseparated. A blend may or may not contain one or more domainconfigurations, as determined from transmission electron spectroscopy,light scattering, x-ray scattering, or any other method known in theart. Preferred blends (e.g., preferred reactor blends) including two ormore phases. For example the blend may include a first phase includingsome or all of the monovinyl aromatic polymer and a second phaseincluding some or all of the rubber. In the context of this invention,blend includes the chemical and/or physical coupling of the monovinylaromatic polymer with the elastomeric polymer, e.g., one polymer isgrafted onto or otherwise incorporated into the other polymer.

As used herein, “composition” and like terms means a mixture or blend oftwo or more components. One composition of this invention is the mix ofmonomers, polymerization initiator and any other components necessary ordesirable to make the monovinyl aromatic polymer, while anothercomposition of this invention is the rubber-modified monovinyl aromaticpolymer including the elastomeric polymer. These compositions mayinclude other components, polymeric or non-polymeric (e.g., additives),necessary or desirable to the end use of the composition.

The compositions according to the teachings herein achieve improvedbalance of performance properties including good environmental stresscrack resistance and generally high modulus. These improvements arepredicated on one or more (or even all) of the following: a generallylow concentration of elastomeric polymer, a generally high concentrationof monovinyl aromatic polymer, a generally high molecular weightmonovinyl aromatic polymer, or a generally larger rubber particle size.

Monovinyl Aromatic Polymers

Monovinyl aromatic homopolymers and copolymers (individually andcollectively referred to as “polymers” or “copolymers”) are produced bypolymerizing monovinyl aromatic monomers such as those described in U.S.Pat. Nos. 4,666,987, 4,572,819 and 4,585,825. The monovinyl aromaticpolymer includes, consists essentially of, or consists entirely of oneor more monovinyl aromatic monomers. The monovinyl aromatic monomerssuitable for producing the polymers and copolymers used in the practiceof this invention are preferably of the following formula:

in which R² is hydrogen or methyl, R¹ is an aromatic ring structurehaving from 1 to 3 aromatic rings with or without alkyl, halo, or haloalkyl substitution, wherein any alkyl group contains 1 to 6 carbon atomsand halo alkyl refers to a halo substituted alkyl group. Preferably, R¹is phenyl or alkyl phenyl (in which the alkyl group of the phenyl ringcontains 1 to 10, preferably 1 to 8 and more preferably 1 to 4, carbonatoms), with phenyl being most preferred. Typical monovinyl aromaticmonomers which may be used include: styrene, alpha-methyl styrene, allisomers of vinyl toluene, especially para-vinyl toluene, all isomers ofethyl styrene, propyl styrene, vinyl biphenyl, vinyl naphthalene, vinylanthracene and the like, and mixtures thereof. Most preferably, themonovinyl aromatic monomer includes, consists essentially of, orconsists entirely of styrene. The concentration of the monovinylaromatic monomers (e.g., the concentration of styrene) preferably isabout 60 weight percent or more, more preferably about 65 weight percentor more, even more preferably about 70 weight percent or more, even morepreferably about 80 weight percent or more, even more preferably about90 weight percent or more, and most preferably about 93 weight percentor more, based on the total weight of the monovinyl aromatic polymer. Asused herein, a monovinyl aromatic polymer that consists essentially ofone or more monovinyl aromatic monomers (e.g., consists essentially ofstyrene) may have a concentration of monovinyl aromatic monomers (e.g.,a concentration of styrene) of about 95 weight percent or more, morepreferably about 98 weight percent or more, even more preferably about99 weight percent or more, and most preferably about 99.5 weight percentor more, based on the total weight of the monovinyl aromatic polymer.

The monovinyl aromatic monomer can be copolymerized with one or more ofa range of other copolymerizable monomers. Preferred comonomers includenitrile monomers such as acrylonitrile, methacrylonitrile andfumaronitrile; (meth)acrylate monomers such as methyl methacrylate orn-butyl acrylate; maleic anhydride and/or N-aryl maleimides such asN-phenyl maleimide, and conjugated and nonconjugated dienes.Representative copolymers include styrene-acrylonitrile (SAN)copolymers. The copolymers typically include the comonomer at aconcentration of about 0.1 weight percent or more, preferably about 1weight percent or more, even more preferably about 2 weight percent ormore, and most preferably about 5 weight percent or more, based onweight of the copolymer. Typically, the copolymer includes the copolymerat a concentration of 40 weight percent or less, preferably about 35weight percent or less, and most preferably about 30 weight percent orless, based on the weight of the copolymer.

The monovinyl aromatic polymer matrix may provide strength and stiffnessto the composition. The monovinyl aromatic polymer matrix preferably issufficiently rigid so that the resulting composition is suitable for usein thin walled parts, even when the composition includes a sufficientquantity of elastomeric polymer so that it has good resistance toenvironmental stress cracking. Preferably, the monovinyl aromaticpolymer matrix is sufficiently rigid so that the composition has aflexural modulus (as measured according to ISO 178 of about 1000 MPa ormore, more preferably about 1500 MPa or more, even more preferably about1600 MPa or more, and most preferably about 1700 MPa or more.Preferably, the monovinyl aromatic polymer matrix is sufficiently rigidso that the composition has a tensile modulus (as measured according toISO 527-1) of about 1000 MPa or more, more preferably about 1400 MPa ormore, even more preferably about 1500 MPa or more, and most preferablyabout 1600 MPa or more

The monovinyl aromatic polymer generally has a high molecular weight.The molecular weight may be characterized by the number averagemolecular weight (M_(n)), the weight average molecular weight (M_(w)),the z-average molecular weight (M_(z)), the polydispersity index, or anycombination thereof. The molecular weight of the monovinyl aromaticpolymer is measured for the fraction of the polymer that is soluble inthe gel permeation chromatography solvent (e.g., in tetrahydrofuran atabout 25° C.). The molecular weight of the monovinyl aromatic polymershould be sufficiently high so that the composition has good resistanceto environmental stress cracking, despite having a low concentration ofrubber (e.g., about 7.5 weight percent or less) and/or a generally highconcentration of monovinyl aromatic polymer (e.g., about 90 weightpercent or more). The weight average molecular weight of the monovinylaromatic polymer preferably is 200,000 g/mol or more, more preferably205,000 g/mol or more, even more preferably 210,000 g/mol or more, andmost preferably 215,000 g/mol or more. The weight average molecularweight of the monovinyl aromatic polymer should be sufficiently low sothat the material can be easily produced and/or processed. The weightaverage molecular weight of the monovinyl aromatic polymer may be about300,000 g/mol or less, about 280,000 g/mol or less, about 260,000 g/molor less, or about 240,000 g/mol or less. It will be appreciated thatpolymers having a weight average molecular weight of about 300,000 g/molor more may also be employed. The monovinyl aromatic polymer preferablyhas a z-average molecular weight of about 300,000 g/mol or more, morepreferably about 330,000 g/mol or more, even more preferably about360,000 g/mol, and most preferably about 390,000 g/mol or more. Themonovinyl aromatic polymer preferably has a z-average molecular weightof about 1,000,000 g/mol or less. The polydispersity index of themonovinyl aromatic polymer should be sufficiently high so that thepolymer has a sufficient concentration of long chains for improving theresistance to environmental stress cracking. Preferably, thepolydispersity index of the monovinyl aromatic polymer is about 2.0 ormore, more preferably about 2.1 or more, even more preferably about 2.3or more, even more preferably about 2.5 or more, even more preferablyabout 2.7 or more and most preferably about 3.0 or more. Thepolydispersity index of the monovinyl aromatic polymer preferably isabout 8 or less, more preferably about 5 or less, and most preferablyabout 4 or less.

The monovinyl aromatic polymer is rubber modified using one or moreelastomeric polymers (present as rubber particles). The elastomericpolymer (i.e., rubber) may be any rubber suitable for improving theimpact resistance and/or the resistance to environmental stress crackingwhen present in a monovinyl aromatic polymer. The elastomeric polymerpreferably is an unsaturated rubbery polymer or other polymer capable offorming a graft copolymer during the polymerization of the monovinylaromatic polymer. The elastomeric polymer preferably has a glasstransition temperature (Tg) of about 0° C. or less, more preferablyabout −10° C. or less, and most preferably about −20° C. or less, asdetermined by ASTM D-756-52T using differential scanning calorimetry.The glass transition temperature is the temperature or temperature rangeat which an elastomeric polymeric material shows an abrupt change in itsphysical properties, including, for example, mechanical strength and/orviscosity.

Exemplary elastomeric polymers include, but are not limited to, dienerubbers, diene block rubbers, butyl rubbers, ethylene-propylene rubbers,ethylene-propylene-diene monomer (EPDM) rubbers, ethylene copolymerrubbers, acrylate rubbers, polyisoprene rubbers, halogen containingrubbers, silicone rubbers and mixtures of two or more of these rubbers.Interpolymers of rubber-forming monomers with other copolymerizablemonomers may also be used. Exemplary diene rubbers include, but are notlimited to, conjugated 1,3-dienes, for example, butadiene, isoprene,piperylene, chloroprene, or mixtures of two or more of these dienes.Exemplary rubbers also include homopolymers of conjugated 1,3-dienes andinterpolymers of conjugated 1,3-dienes with one or more copolymerizablemonoethylenically unsaturated monomers, for example, copolymers ofisobutylene and isoprene. Particularly preferred elastomeric polymersinclude, consist essentially of, or consist entirely of butadiene. Forexample, the concentration of butadiene in the elastomeric polymer maybe about 10 weight percent or more, about 30 weight percent or more,about 50 weight percent or more, about 70 weight percent or more, about75 weight percent or more, or about 90 weight percent or more, based onthe total weight of the elastomeric polymer.

Preferred elastomeric polymers include diene rubbers such aspolybutadiene, polyisoprene, polypiperylene, polychloroprene, and thelike or mixtures of diene rubbers, i.e., any rubbery polymers of one ormore conjugated 1,3-dienes, with 1,3-butadiene being especiallypreferred. Such rubbers include homopolymers and copolymers of1,3-butadiene with one or more copolymerizable monomers, such asmonovinyl aromatic monomers as described above, styrene being preferred.Preferred copolymers of 1,3-butadiene are block or tapered block rubbersincluding i) about 30 weight percent, more preferably about 50 weightpercent or more, even more preferably at about 70 weight percent ormore, and most preferably about 90 weight percent or more 1,3-butadienerubber, and ii) about 70 weight percent or less, more preferably about50 weight percent or less, even more preferably about 30 weight percentor less, and most preferably about 10 weight percent or less monovinylaromatic monomer; where all weights based on the total weight of the1,3-butadiene copolymer. Preferred elastomeric polymers have a solutionviscosity in the range of about 5 to about 300 cP (5 percent by weightin styrene at 20° C.) and/or a Mooney viscosity of about 5 to about 100(ML 1+4, 100° C.), for example as measured according to ASTM D 1646.

The elastomeric polymer in the rubber-modified polymers of thisinvention, for purposes of maintaining reduced cost and good physicalproperty combinations (e.g., high modulus) may be present in an amountof about 10 weight percent or less, preferably about 8 weight percent orless, more preferably about 7.5 weight percent or less, even morepreferably about 7.3 weight percent or less, even more preferably about7.1 weight percent or less, and most preferably about 6.9 weight percentor less based on the total weight of the composition and/or based on theweight of rubber modified polymer. The elastomeric polymer is typicallypresent in an amount as needed to provide sufficient toughness andtensile strength for a given application and/or sufficient resistance toenvironmental stress cracking. The elastomeric polymer may be present inan amount of about 1 weight percent or more, preferably about 2 weightpercent or more, more preferably about 3 weight percent or more, evenmore preferably about 4 weight percent or more, and most preferablyabout 5 weight percent or more, based on the total weight of thecomposition and/or based on the total weight of rubber modifiedmonovinyl aromatic polymer. Typically, HIPS products contain less rubberthan ABS products.

Preferably, the concentration of the elastomeric polymer is sufficientlyhigh and/or the concentration of the mineral oil is sufficiently high sothat the composition has a tensile modulus (as measured according to ISO527-1) of about 2200 MPa or less, more preferably about 2000 MPa orless, even more preferably about 1950 MPa or less, and most preferablyabout 1900 MPa or less. Preferably, the concentration of the elastomericpolymer is sufficiently high and/or the concentration of the mineral oilis sufficiently high so that the composition has a flexural modulus (asmeasured according to ISO 178) of about 2200 MPa or less, morepreferably about 2000 MPa or less, even more preferably about 1950 MPaor less, and most preferably about 1900 MPa or less.

The elastomeric polymer preferably is present as rubber particles. Someor all of the rubber particles may be present as grafted and/or occludedrubber particles dispersed in the monovinyl aromatic polymer matrix. Therubber particles preferably are cross-linked. The cross-linking may becharacterized by the light absorption ratio (i.e., Brinkmann). Theelastomeric polymer in the composition preferably has a cross-linkdensity that is sufficiently high so that the light absorption ratio(Brinkmann) is about 0.5 or more, more preferably about 0.55 or more,and most preferably about 0.6 or more. The elastomeric polymerpreferably have a cross-link density that is sufficiently low so thatthe light absorption ratio (Brinkmann) is about 0.80 or less, morepreferably about 0.75 or less, and most preferably about 0.70 or less

The rubber particles in the compositions according to the presentinvention should have a particle size sufficiently high large so thatthe composition has good resistance to environmental stress cracking.The rubber particles preferably have a volume average diameter of atleast about 3 micrometers or more, more preferably about 4 μm or more,even more preferably about 5 μm or more, and most preferably about 6 μmor more. Such rubber particles have a surprisingly high particle sizeparticularly for compositions having a low concentration of elastomericpolymer and a monovinyl aromatic polymer having a high molecular weight.High rubber particle size may be achieved using a process that includesa first reaction step that polymerizes some of the monovinyl aromaticmonomer and produces rubber particles of sufficiently high diameter, andan additional reaction step that increases the molecular weight of themonovinyl aromatic polymer without significantly reducing the size ofthe rubber particles. The volume average diameter of the rubberparticles preferably is about 30 μm or less, more preferably about 20 μmor less, even more preferably about 15 μm or less, even more preferablyabout 10 μm or less, and most preferably about 8 μm or less. As usedherein, the volume average rubber particle size or diameter refers tothe diameter of the rubber particles, including all occlusions andgrafts. Particle sizes in these ranges can typically be measured usingthe electro sensing zone method, such as the “Multisizer” brandequipment provided by Beckman Coulter, Inc. or using measurementtechniques based on light scattering (Malvern Mastersizer, BeckmanCoulter LS 230). If needed, transmission electron microscopy analysiscan be used for rubber particle size and morphology analysis. Thoseskilled in the art recognize that different sized groups of rubberparticles may require some selection or modification of rubber particlemeasurement techniques for optimized accuracy.

The compositions of this invention can further comprise one or morefillers and/or additives as long as they do not detrimentally affect thedesired property combinations that are otherwise obtained or,preferably, they would improve one or more of the properties. Forexample, plasticizers (preferably mineral oil) is one such additive forHIPS that may improve the ESCR of HIPS. These materials are added inknown amounts using conventional equipment and techniques. Otherrepresentative fillers include talc, calcium carbonate, organo-clay,glass fibers, marble dust, cement dust, feldspar, silica or glass, fumedsilica, silicates, alumina, various phosphorus compounds, ammoniumbromide, antimony trioxide, antimony trioxide, zinc oxide, zinc borate,barium sulfate, silicones, aluminum silicate, calcium silicate, titaniumoxides, glass micro spheres, chalk, mica, clays, wollastonite, ammoniumoctamolybdate, intumescent compounds, expandable graphite, and mixturesof two or more of these materials. The fillers may carry or containvarious surface coatings or treatments, such as silanes, fatty acids,and the like. As discussed above, the composition may optionally includea plasticizer. Preferably, the concentration of the plasticizer (e.g.,the concentration of the mineral oil) is greater than 2 weight percent,more preferably about 2.3 weight percent or more, and most preferablyabout 2.6 weight percent or more, based on the total weight of thecomposition. The concentration of the plasticizer (e.g., theconcentration of the mineral oil), if employed, is preferably about 8weight percent or less, more preferably about 6 weight percent or less,even more preferably about 5 weight percent or less, even morepreferably about 4 weight percent or less, and most preferably about 3.6weight percent or less, based on the total wait of the composition.

Still other additives include flame retardants such as the halogenatedorganic compounds. The composition can also contain additives such as,for example, antioxidants (e.g., hindered phenols such as, for example,IRGANOX® 1O76 a registered trademark of BASF resins), mold releaseagents, processing aids other than mineral oil (such as other oils,organic acids such as stearic acid, metal salts of organic acids),colorants or pigments to the extent that they do not interfere withdesired physical or mechanical properties of the compositions of thepresent invention.

Process for Preparing the Rubber Modified Polymer

Although any of the generally well-known processes to make therubber-modified monovinyl aromatic polymers can be used, a preferredprocess is based on polymerizing monovinyl aromatic monomer(s) (and anyoptional comonomer) to make the polymer in the presence of the rubber.The process may use one or more reactors and/or one or more reactionzones. For example, the process may include multiple reactors and/ormultiple reaction zones connected in series. As known to those skilledin the art, these reactors/zones can use the same or differentinitiators/reactants and/or be operated at different conditions, e.g.,different reactant concentrations, temperatures, pressures, etc. toprovide a range of features and variations in the monovinyl aromaticpolymers. This process provides a desirable rubber-modified monovinylaromatic polymer composition comprising a dispersion of rubberparticles, preferably grafted with monovinyl aromatic polymer, in themonovinyl aromatic polymer matrix. The process may include one or anycombination of the steps and/or features described in U.S. Pat. No.4,144,204 (see for example column 2, line 21 to column 8, line 16), U.S.Pat. No. 4,666,987 (see for example column 2, line 56 to column 5, line52), U.S. Pat. No. 4,572,819 (see for example, FIG. 1, FIG. 2, FIG. 3,and column 2, line 25 to column 7, line 57), and U.S. Pat. No. 4,585,825(see e.g., FIG. 1, FIG. 2, FIG. 3, FIG. 4, and column 4, line 44 tocolumn 21, line 24), U.S. Pat. No. 6,353,066 B1 (see e.g., FIG. 1, FIG.2, FIG. 3, and column 2, line 18 to column 5, line 24), U.S. Pat. No.6,350,813 (see for example column 1, line 66 to column 6, line 48), andUS Patent Application Publication No. US2011/218292 (see for exampleparagraphs 0018 to 0068) all incorporated herein by reference in theirentirety.

The process may include one or more steps of cross-linking the rubber. Across-linking step may occur at any time in the process (e.g., before,after, or during the polymerization of the monovinyl aromatic monomer)Preferably, the process includes a crosslinking reaction following astep of polymerizing the monovinyl aromatic monomer. For example, acrosslinking reaction of the rubber may take place during the formationof the product, during a devolatilization step, or both.

The concentration of the elastomeric polymer preferably is sufficientlylow so that the composition has a high tensile modulus that allows fordown gauging without compromising the mechanical performance. Theconcentration of the elastomeric polymer may be sufficiently low so thatthe composition has a tensile modulus of about 1400 MPa or more,preferably about 1500 MPa or more, and most preferably about 1600 MPa ormore.

The compositions according to the teachings herein may be characterizedby one or more (e.g., two or more, three or more, or even all) of thefollowing: a melt flow rate of about 50 g/10 min or less (preferablyabout 10 g/10 min or less, and more preferably about 5 g/10 min orless); a melt flow rate of about 0.5 g/10 min or more (preferably about1 g/10 min or more, and more preferably about 2 g/10 min or more); aVicat softening point (measured at 120/1) of about 60° C. or more, morepreferably about 75° C. or more, and most preferably about 90° C. ormore); a tensile yield of about 12.0 MPa or more (preferably about 14.5or more, more preferably about 15.5 MPa or more, and most preferablyabout 16.0 MPa or more); a tensile elongation of about 30% or more(preferably about 40% or more, and more preferably about 50% or more);an tensile modulus of about 1000 MPa or more (preferably about 1400 MPaor more, more preferably about 1500 MPa or more, and most preferablyabout 1600 MPa or more); a Notched Izod measured at −20° C. of about 3kJ/m² or more (preferably about 4 kJ/m² or more, and more preferablyabout 5 kJ/m² or more); or a heat distortion temperature (measured witha stress of 0.45 MPa) of about 60° C. or more (preferably about 70° C.or more, more preferably about 80° C. or more).

Particularly preferred compositions are substantially free of, orentirely free of thermoplastic polyolefins having a melting temperaturegreater than or equal to 50° C. and/or a crystallinity of about 10% ormore. For example, the composition may be substantially free of, orentirely free of one or any combination of the following thermoplasticpolyolefins: polyethylenes, polypropylenes, ethylene/α-olefincopolymers, or propylene α-olefin copolymers. If present, theconcentration of any thermoplastic polyolefin preferably is about 5weight percent or less, more preferably about 2 weight percent or less,even more preferably about 1 weight percent or less, and most preferablyabout 0.5 weight percent or less.

Applications

The compositions according to the teachings herein may be formed into anarticle using any forming and/or shaping process. For example, thecomposition may be formed into an article using a process that includesextrusion, injection molding, blow molding, casting, thermoforming, orany combination thereof. The article may be in any form generally usedin forming polymer compositions. Without limitation, the article may bea film, a fiber, a sheet structure, a molded object, a blow moldedobject, an extruded profile, a thermoformed shape, and the like. Thecompositions may be used in transportation (e.g., automotive) or othernon-transportation applications such as industrial applications andappliance applications. The compositions according to the teachingsherein may be used in hoses, refrigerator liners and other liners(appliance or otherwise), clothing and footwear components, gaskets andthe like.

Test Methods Molecular Weight Distribution

Unlike small molecules, the molecular weight of a polymer is generallynot one unique value. Rather, a given polymer will have a molecularweight distribution. The distribution generally will depend on the waythe polymer is produced. For polymers the distribution of molecularweight is a function P(M), where P(Mi) is the probability, or fractionof molecules having a molecular weight Mi. As used herein, molecularweight distribution describes the distribution of the molecular weightof a polymer. The molecular weight of the monovinyl aromatic polymer,refers to the molecular weight of the soluble fraction of the matrix.The molecular weight may be measured using gel permeationchromatography. Different solvents can be used, a typical solvent istetrahydrofuran. Polystyrene standards may be used for calibration. Theaverage molecular weight may be characterized by the number averagemolecular weight (i.e., Mn), the weight average molecular weight (i.e.,Mw), the z-average molecular weight (i.e., Mz), or any combinationthereof. The polydispersity index is defined as the ratio of the weightaverage molecular weight, Mw, and the number average molecular weight,Mn.

Swelling Index

The swelling index, Q, is measured according to the method described inU.S. Pat. No. 4,144,204 (column 5, lines 35-54). The composition isplaced in toluene at 25° C. After the soluble polymer dissolves in thetoluene, the solution is centrifuged to separate the liquid polymersolution and the undissolved polymer (e.g., the insoluble gelconstituent). After centrifuging, the liquid is decanted, thus isolatingthe swollen insoluble polymer (i.e., the wet gel). The mass of the wetgel is measured. The wet gel is dried to remove the toluene. The mass ofthe dry gel is then measured. The swelling index, Q, is defined as theratio of mass of the wet gel to the mass of the dry gel. The swellingindex is related to the concentration of cross-links in the rubberparticles. A high swelling index is characteristic of a polymer having alow concentration of cross-links. A low swelling index is characteristicof a polymer having a high concentration of cross-links.

Gel Content

The gel content is a measure for the amount cross-linked rubber, graftlayer and occlusions. The composition is initially weighted and thenheated under nitrogen to a temperature of about 280° C. for about 2hours to fully cross-link the rubber. The composition is then placed intoluene at 25° C. The toluene and soluble polymer is removed. Theremaining gel is dried and then reweighed. The gel content is the weightpercent of the composition that remains in the dried gel, expressed inunits of weight percent.

Light Absorbance Ratio (i.e., LAR)

The amount of rubber cross-linking may be quantified by the lightabsorbance ratio (LAR). LAR is the ratio of light absorbance for asuspension of the rubber particles in dimethyl formamide (DMF) and thelight absorbance for a suspension of the rubber particles indichloromethane (DCM). LAR may be determined using a Brinkmann model PC800 probe colorimeter equipped with a 450 nm wavelength filter, fromBrinkmann Instruments Inc., Westbury, N.Y., or equivalent. In a firstvial, a 0.4 gram (g) sample of rubber-modified copolymer is dissolved in40 milliliters (ml) DMF. From the first vial, 5 ml of the resulting DMFsolution is added to a second vial containing 40 ml of DMF. From thefirst vial, 5 ml of the resulting DMF solution is added to a third vialcontaining 20 ml DCM. The probe is zeroed in neat DMF. The absorption ofthe DMF solution (i.e., A_(DMF)) in the second vial and the absorptionof the DCM solution (i.e., A_(DCM)) in the third vial are determined.The light absorbance ratio is calculated by the following equation:

LAR=A _(DMF) /A _(DCM)

Melt Flow Rate

The melt flow rate of the composition is measured according to ISO 1133,Condition G at 200° C./5 kg.

Tensile Properties

The tensile modulus (i.e., elastic modulus), the tensile elongation, andthe tensile rupture are all measured according to ISO 527-2. Theelongation rate may be about 50 mm/min (e.g., for ABS) or about 5 mm/min(e.g., for HIPS). Test specimens may be conditioned at 23° C. and 50percent relative humidity 24 hours prior to testing. Testing may beperformed at 23° C. using a Zwick Z010 mechanical tester, or equivalenttesting apparatus. Unless otherwise stated, tensile properties aremeasured on injection molded samples, with the length of the sample inthe strong direction.

Flexural Modulus

The flexural modulus is measured according to ISO 178. Unless otherwisestated, flexural modulus is measured on injection molded samples, withthe length of the sample in the strong direction.

Charpy Impact Strength

The Charpy Impact Strength is measured according to ISO 148 using a testspecimen having dimensions 10 mm×10 mm×55 mm at a test temperature of23° C. or −20° C. Notched (V-notch) Charpy is determined according tothe ISO 179 1eA at 23° C.

Izod Impact Strength

The Notched Izod impact resistance is measured according to ISO 180/1Aat a test temperature of 23° C. or −20° C. Notched Izod may bedetermined according to one of the following standards: ISO 180/1.

Vicat Softening Temperature

The Vicat softening temperature is a measured according to ISO 306 at aheating rate 120° C./hour and a load of 10 N.

Heat Deflection Temperature

The heat deflection temperature is measured according to ISO 78.

Rubber Particle Size

The rubber particle size is measured using Coulter Multisizer II or IIeusing the electrosensing technique. The set-up may employ the ACCUCOMP™Software Version 2.01. About 3 granules of polymer samples (30-70 mg) isdissolved in 5 ml of DMF, using sonication for approximately 15 to 20minutes. About 10 ml of an electrolyte solution (1 percent NH₄SCN inDMF) is mixed with 0.2 ml of the sample solution. The appropriateCoulter tube (e.g. for HIPS=30 μm aperture) is used in combination witha calibration material. The coincidence level indicator of the apparatusshould read between 5 and 10 percent. If the coincidence level is above10 percent, the sample solution is diluted with electrolyte solution. Ifthe coincidence level is too low, more drops of the polymer solution inDMF is added. The volumetric mean particle size is reported inmicrometer (μm).

ESCR (Resistance to Environmental Stress Cracking)

“ESCR” is measured consistent with International Standard ISO-4599. Testspecimens are molded for tensile testing consistent with ISO-527. Thetest procedure requires measuring a tensile property (e.g., elongationat break) of the test specimens (bars) of the candidate resin(s) beforeand after they are immersed in corn oil under measured strain. Thetemperature during the test is 23±2° C., and the test bar samples areclamped into a frame that applies 1.0% strain (sometimes 0.5% strain isapplied). The test bar, being held under strain in the frame, is heldsubmerged in corn oil for n days (where n is 4 and 10 days). After thespecified time, the bars are removed from the corn oil, removed from theframe, cleaned and tested using tensile testing. The percentageelongation at break, stress at failure, stress at yield, and tensilemodulus are measured. From the before and after tensile test (e.g.,elongation test) results, the retention percentage is calculated bydividing the tensile test value of the ESCR sample by the tensile testvalue for the unsubmerged bar, and then multiply by 100 to convert tounits of percent. This property retention value is referred to as the“environmental stress crack resistance” and is shown as “ESCR 1% strain”or “ESCR 0.5% strain” depending on the strain applied. The criterion forgenerally successful or sufficient ESCR performance is that testspecimens exposed at 1% strain after 10 days immersion retain at least15%, and preferably at least about 30% of the value of the testedtensile property (e.g., elongation) measured on unexposed testspecimens.

Rubber Concentration/Composition

The composition of the resin may be determined using Fourier Transforminfrared spectroscopy. The sample may be pressed or otherwisetransformed into a thin film. This technique may be employed to measurethe amount of acrylonitrile (i.e., AN), N-phenyl maleimide (i.e.,N-PMI), n-butyl acrylate (i.e., nBA), polybutadiene, or any combinationthereof. For example infrared spectroscopy may be used to determine theamount of polybutadiene originating from the rubber.

The amount of polybutadiene may also be determined using a titrationtechnique. For example, a known amount of sample may be dissolved inortho-dichlorobenzene. A known amount of solution of Wijs is added whichreacts with the unsaturated bonds of the polybutadiene present in thesample. After 60 min of reacting in the dark the amount of Iodinemonochloride which did not react is reacted with potassiumiodide toiodine. The iodine may then be titrated with sodiumthiosulfate. Thepolybutadiene content may be calculated from the amount ofsodiumthiosulfate needed to titrate the iodine.

Any numerical values recited herein include all values from the lowervalue to the upper value in increments of one unit provided that thereis a separation of at least 2 units between any lower value and anyhigher value. As an example, if it is stated that the amount of acomponent or a value of a process variable such as, for example,temperature, pressure, time and the like is, for example, from 1 to 90,preferably from 20 to 80, more preferably from 30 to 70, it is intendedthat values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. areexpressly enumerated in this specification. For values which are lessthan one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 asappropriate. These are only examples of what is specifically intendedand all possible combinations of numerical values between the lowestvalue and the highest value enumerated are to be considered to beexpressly stated in this application in a similar manner. As can beseen, the teaching of amounts expressed as “parts by weight” herein alsocontemplates the same ranges expressed in terms of percent by weight.Thus, an expression in the Detailed Description of the Invention of arange in terms of at “‘x’ parts by weight of the resulting polymericblend composition” also contemplates a teaching of ranges of samerecited amount of “x” in percent by weight of the resulting polymericblend composition.”

Unless otherwise stated, all ranges include both endpoints and allnumbers between the endpoints. The use of “about” or “approximately” inconnection with a range applies to both ends of the range. Thus, “about20 to 30” is intended to cover “about 20 to about 30”, inclusive of atleast the specified endpoints.

The disclosures of all articles and references, including patentapplications and publications, are incorporated by reference for allpurposes. The term “consisting essentially of” to describe a combinationshall include the elements, ingredients, components or steps identified,and such other elements ingredients, components or steps that do notmaterially affect the basic and novel characteristics of thecombination. The use of the terms “comprising” or “including” todescribe combinations of elements, ingredients, components or stepsherein also contemplates embodiments that consist essentially of theelements, ingredients, components or steps.

Plural elements, ingredients, components or steps can be provided by asingle integrated element, ingredient, component or step. Alternatively,a single integrated element, ingredient, component or step might bedivided into separate plural elements, ingredients, components or steps.The disclosure of “a” or “one” to describe an element, ingredient,component or step is not intended to foreclose additional elements,ingredients, components or steps.

It is understood that the above description is intended to beillustrative and not restrictive. Many embodiments as well as manyapplications besides the examples provided will be apparent to those ofskill in the art upon reading the above description. The scope of theinvention should, therefore, be determined not with reference to theabove description, but should instead be determined with reference tothe appended claims, along with the full scope of equivalents to whichsuch claims are entitled. The disclosures of all articles andreferences, including patent applications and publications, areincorporated by reference for all purposes. The omission in thefollowing claims of any aspect of subject matter that is disclosedherein is not a disclaimer of such subject matter, nor should it beregarded that the inventors did not consider such subject matter to bepart of the disclosed inventive subject matter.

EXAMPLES

Example 1 is prepared using a sufficient amount of polybutadiene rubberto result in a final rubber concentration of 7.8 weight percent in thefinal composition. Styrene monomer is polymerized in the presence of therubber under dynamic conditions for controlling the rubber particlesize, after phase inversion, as the polymerization proceeds. Thepolymerization of the styrene results in monovinyl aromatic polymer thatis grafted to the rubber and monovinyl aromatic polymer that is notgrafted to the rubber. At an early time in the polymerization, there areno rubber particles, and the rubber phase is the continuous phase. Atthis early time the polystyrene is present as particles. At a latertime, after phase inversion, the polystyrene becomes the continuousphase and the rubber phase is present as a discontinuous phase (i.e.,discrete particles). About 3.0 weight percent mineral oil is present inthe rubber-modified monovinyl aromatic polymer, being added prior to thepolymerization of the styrene. The composition and properties of Example1 are shown in Table 1 and Table 2 below.

Example 2

Example 2 is prepared using a sufficient amount of polybutadiene rubberto result in a final rubber concentration of 6.6 weight percent in thefinal composition. Styrene monomer is polymerized in the presence of therubber under dynamic conditions for controlling the rubber particlesize, after phase inversion, as the polymerization proceeds. Thepolymerization of the polystyrene results in monovinyl aromatic polymerthat is grafted to the rubber particles and monovinyl aromatic polymerthat is not grafted to a rubber particle. At an early time in thepolymerization, there are no rubber particles, and the rubber phase isthe continuous phase. At this early time the polystyrene is present asparticles. At a later time, after phase inversion, the polystyrenebecomes the continuous phase and the rubber phase is present as adiscontinuous phase. About 2.7 weight percent mineral oil is present inthe rubber-modified monovinyl aromatic polymer, being added prior to thepolymerization of the styrene. The composition and properties of Example2 are shown in Table 1 and Table 2 below. The flexural modulus ofExample 2 is increased by about 10% or more (e.g., about 15% or more)compared with Example 1. The tensile modulus of Example 2 is increasedby about 10% or more (e.g., about 15% or more) compared with example 1.Despite having a generally high concentration of monovinyl aromaticpolymer and a generally low concentration of elastomeric polymer,Example 2 has improved resistance to environmental stress crackingcompared with Example 1, as shown by the increase in retention ofproperties after immersion in corn oil at 4 and 10 days.

TABLE 1 Example 1 Example 2 Composition Monovinyl aromatic polymer wt. %89.2 90.7 Elastomeric polymer wt. % 7.8 6.6 Mineral Oil wt. % 3.0 2.7Elastomeric Polymer Type Polybutadiene Polybutadiene Monovinyl aromaticmonomer Type Styrene Styrene Properties of soluble monovinyl aromaticpolymer Molecular weight Mz g/mol 280,000-330,000 437,000 Mw g/mol160,000-197,000 217,000 Mn g/mol 75,000-98,000 68,500 PolydispersityIndex 2.00-2.08 3.16 Properties of composition Melt flow rate g/10 min2.6 3.6 Gel content % 31.1 27.8 Swelling index % 10.9 11.7 LightAbsorbance Ratio 0.67 0.69 Heat deflection temperature Measured at 0.45MPa ° C. 81 82 Measured at 1.82 MPa ° C. 68 67 Vicat softening point(120/1) ° C. 98 98 Impact strength, notched Izod Measured at 23° C.kJ/m² 10.8 8.6 Measured at −20° C. kJ/m² 8.2 6.0 Impact strength,notched Charpy Measured at 23° C. kJ/m² 10.7 8.1 Measured at −20° C.kJ/m² 7.8 6.3 Tensile Properties Stress at yield MPa 14.2 16.6 Stress atrupture MPa 22.3 22.5 Elongation (at rupture) % 94 56 Elastic ModulusMPa 1390 1630 Flexural Properties Elastic Modulus MPa 1515 1800

TABLE 2 Environmental Stress Crack Resistance Example 1 Example 2 ESCR(corn oil, 4 days, 0.5% strain) Measured Tensile Properties Stress atyield MPa 14.1 16.8 Stress at rupture MPa 19.3 20.3 Elongation (atrupture) % 55 36 Elastic Modulus MPa 1340 1640 Retention of TensileProperties Stress at yield % retention 99 101 Stress at rupture %retention 87 90 Elongation (at rupture) % retention 59 64 ElasticModulus % retention 96 101 ESCR (corn oil, 4 days, 1% strain) MeasuredTensile Properties Stress at yield MPa 13.5 16.2 Stress at rupture MPa15.7 19.9 Elongation (at rupture) Percent 26 34 Elastic Modulus MPa 13001580 Retention of Tensile Properties Stress at yield % retention 95 98Stress at rupture % retention 70 88 Elongation (at rupture) % retention28 61 Elastic Modulus % retention 94 97 ESCR (corn oil, 10 days, 0.5%strain) Measured Tensile Properties Stress at yield MPa 13.9 16.6 Stressat rupture MPa 18.8 20.4 Elongation (at rupture) % 54 37 Elastic ModulusMPa 1380 1665 Retention of Tensile Property Stress at yield % retention98 100 Stress at rupture % retention 84 91 Elongation (at rupture) %retention 57 66 Elastic Modulus % retention 99 102 ESCR (corn oil, 10days, 1% strain) Measured Tensile Properties Stress at yield MPa 13.416.0 Stress at rupture MPa 16.5 21.3 Elongation (at rupture) % 36 45Elastic Modulus MPa 1340 1605 Retention of Tensile Property Stress atyield % retention 94 96 Stress at rupture % retention 74 95 Elongation(at rupture) % retention 38 80 Elastic Modulus % retention 96 98

What is claimed is:
 1. A composition comprising: a rubber-modifiedmonovinyl aromatic polymer including i) about 90 weight percent or moreof a rigid monovinyl aromatic polymer matrix, based on the total weightof the composition; and ii) from about 2 to about 7.5 weight percent ofone or more elastomeric polymers, based on the total weight of thecomposition, wherein the one or more elastomeric polymers arecross-linked so that the Brinkmann light absorption ratio is 0.5 ormore; wherein the monovinyl aromatic polymer includes one or moremonovinyl aromatic monomers, and the monovinyl aromatic polymer has asufficiently high molecular weight so that the retention in theelongation at break after 10 days in corn oil at 1% strain is about 15%or more; and wherein the molecular weight of the monovinyl aromaticpolymer is characterized by a weight average molecular weight of 200,000g/mol or more and the molecular weight distribution of the monovinylaromatic polymer is characterized by a polydispersity index of 2.7 ormore.
 2. The composition of claim 1, wherein the monovinyl aromaticpolymer has a weight average molecular weight of 205,000 g/mol or more.3. The composition of claim 1 wherein the elastomeric polymer is presentas grafted and cross-linked rubber particles dispersed within themonovinyl aromatic polymer matrix.
 4. The composition of claim 2 whereinthe one or more monovinyl aromatic monomers includes styrene.
 5. Thecomposition of claim 1 wherein the rubber-modified monovinyl aromaticpolymer is a reactor blend having the one or more monovinyl aromaticmonomers polymerized in the presence of the one or more elastomericpolymers.
 6. The composition of claim 1 wherein the molecular weightdistribution of the monovinyl aromatic polymer is characterized by apolydispersity index of 3.0 or more.
 7. The composition of claim 1wherein the monovinyl aromatic polymer includes about 60 weight percentor more styrene, based on the total weight of the monovinyl aromaticpolymer.
 8. The composition of claim 7, wherein the monovinyl aromaticpolymer includes about 95 weight percent or more styrene.
 9. Thecomposition of claim 7, wherein the concentration of the elastomericpolymer is sufficiently low so that the composition has a tensilemodulus of about 1600 MPa or more.
 10. (canceled)
 11. The composition ofclaim 1, wherein the composition includes greater than 2 weight percentplasticizer, based on the total weight of the composition.
 12. Thecomposition of claim 7, wherein the composition has a light absorbanceratio of about 0.5 or more.
 13. The composition of claim 12, wherein thecomposition has a light absorbance ratio of about 0.75 or less.
 14. Thecomposition of claim 1, wherein the monovinyl aromatic polymer ischaracterized by a z-average molecular weight of about 360,000 g/mol ormore.
 15. The composition of claim 1, wherein the concentration of theelastomeric polymer is 7.1 weight percent or less, based on the totalweight of the composition.
 16. The composition of claim 15, wherein theconcentration of the elastomeric polymer is about 4 weight percent ormore based on the total weight of the composition.
 17. The compositionof claim 16, wherein the elastomeric polymer includes at least 75 weightpercent butadiene monomer based on the total weight of the elastomericpolymer.
 18. A refrigerator liner including a composition of claim 1.19. The refrigerator liner of claim 18, wherein the refrigerator lineris characterized by ESCR performance determined by retention inelongation at break after 10 days in corn oil at 1% strain of about 15%or more.
 20. A process including a step of extruding and/orthermoforming a refrigerator liner using the composition of claim
 1. 21.The composition of claim 1, wherein the monovinyl aromatic polymer ischaracterized by a weight average molecular weight of 205,000 g/mol ormore; the molecular weight distribution of the monovinyl aromaticpolymer is characterized by a polydispersity index of 3.0 or more; themonovinyl aromatic polymer includes about 95 weight percent or morestyrene, based on the total weight of the monovinyl aromatic polymer;the concentration of the elastomeric polymer is sufficiently low so thatthe composition has a tensile modulus of about 1700 MPa or more; thecomposition includes greater than 2 weight percent plasticizer, based onthe total weight of the composition; the composition has a lightabsorbance ratio is about 0.75 or less; the monovinyl aromatic polymeris characterized by a z-average molecular weight of about 360,000 g/molor more; the concentration of the elastomeric polymer is 7.1 weightpercent or less, based on the total weight of the composition. theconcentration of the elastomeric polymer is about 4 weight percent ormore based on the total weight of the composition; and the elastomericpolymer includes at least 75 weight percent butadiene monomer based onthe total weight of the elastomeric polymer.